Conventional tape drive data storage systems employ various error correction and recovery methods to detect and correct data errors which, if left unresolved, would compromise the integrity of information read from or written to the magnetic tape media. For example, magnetic recording systems have inherent noises that cause recording bit errors to occur. These noises include such things as poor recording signal, media defects, electronic system noise, and other conditions that interfere with head/media data transfer operations.
Error correction and recovery may be thought of as two distinct operations that are employed at different stages of error processing. Error correction is conventionally implemented using error correction coding (ECC) techniques in which random host data to be placed on a tape medium is encoded in a well-defined structure by introducing data-dependent redundancy information. The presence of data errors is detected when the encoded structure is disturbed. The errors are corrected by making minimal alternations to reestablish the structure. ECC error correction is usually implemented “on-the-fly” as data is processed by the tape drive apparatus. The well-known Reed-Solomon code is one cyclic encoding scheme which has been proposed for ECC error correction. Other encoding schemes are also known in the art.
The capability of the ECC is fixed for any given recording system. For instance, a portion of the ECC capability is devoted to errors received while recording the data. This component is referred to as “Write Margin”. The remainder of the capability is budgeted for reading data at a later time when additional error may occur due to minor tape damage or aging. The amount of ECC left for reading is called “Read Margin”.
The greater the read margin the more reliable a tape drive system is for retrieving the customer's data. As read margin is increased, write margin is decreased causing an increase in write errors that resort to timely error recovery or permanent write errors. A recording system should provide sufficient write margin to maintain performance across a mix of media and hardware. Accordingly, the read and write margin limits are set at a fixed level. The fixed limit may generate tapes that have few errors having close to limit margin and not utilizing additional space on tape reserved for error recovery.
Therefore, it is desirable to utilize additional space on a magnetic tape to increase read margin.